The beta spectrum of tritium has been studied with a pi square root (13)/2-spectrometer. The source consisted of tritium in the atomic form embedded in a metal-dioxide lattice. The measured spectrum was analysed down to 14 keV. All fitting parameters used, in addition to the mass parameter mnu , could be checked by independently determined physical values. No evidence for a non-vanishing antineutrino mass or a mixed state with a heavy antineutrino admixture in the mass region from 0.010 to 4 keV/c2 was found. Typical upper limits for the amplitude were 1.8*10-3 for a 3 keV/c2 and 16*10-3 for a 0.6 keV/c2 heavy neutrino branch at 95% confidence. The value of the electron antineutrino mass was determined to be mnu =15-15+32 eV/c2. The mass difference Delta M(3H-3He) was found to be 18597+or-14 eV/c2. Experimental effects influencing the determination of the rest mass are discussed and considered in the results.

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Inelastic electron scattering from Ca has been performed over a momentum transfer range from 0.6 to 3.0 fm ' in both forward and backward directions. Form factors have been obtained for 25 levels up to 10 MeV excitation. Charge and current densities for 11 low lying electric transitions and current densities for two magnetic transitions have been reconstructed in Fourier Bessel analysis. Three high spin states observed in the region of 9 MeV excitation are found to have the dominant configuration v(lg9&z, lf7/p) but with a total strength of only 36% predicted for the first 8 in a random-phase-approximation calculation. This is interpreted as evidence for particlephonon coupling. Comparisons of the extracted densities are made with random-phaseapproximation calculations using a zero-range, density-dependent Migdal interaction.

Electron scattering cross sections for Zr have been measured with a resolution of less than 40 keV in a momentum transfer range between 0.4~q~3.1 fm ' both at forward angles and at 160', which allows a separation of longitudinal and transverse form factors. The analysis of the positiveparity states (including previous data for some of the states) results in transition densities. Most densities are compared to various model calculations. The density of the 8+ level is used to determine the radius of the g9g2 proton orbit as 8 (g9gg) =5.035+0.045 fm.

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